In a herd of approximately 1,000 hogs, evaluation of muscle specimens collected at various intervals during a 12-year period (1973 to 1985) indicated continuous transmission of Trichinella spiralis. The farm''s rat population and the incidence of trichinosis in the rats was high during 1974, but diminished markedly by 1978. In January 1984, a longitudinal investigation, using tracer pigs, was performed to determine whether rodents and/or other wild animals were involved in transmission of T. spiralis on this farm. Tracer pigs exposed to rodents and wild animals did not become infected with T. spiralis. The rodent population on the farm was small and none of the rodents trapped and examined were found to be infected. Hog cannibalism also was evaluated as a mode of T. spiralis transmission. Results of the investigation indicated that hog cannibalism was the mode of transmission for trichinosis in the herd.